Directed audio systems allow a user to be located at nearly any point within an area and to listen to selected audio content while preventing others in the same area from hearing much or any of the audio content, without the aid of attachments such as headphones or any similar speaker based devices attached to the person or clothing of the user. A simple version of such a technology might be an array of speakers in a ceiling such that only one or more selected speakers located over the listener's location plays the audio content while all other speakers are silent, or alternatively play other audio content for other listeners. Another example of such technology is HyperSonic Sound (HSS)1, a technology used in products marketed by American Technology Corporation. HSS products convert an audio signal into a complex ultrasonic signal that is radiated from a transducer emitter. The signal may be tightly focused because it is highly directional. A listener in the path of the beam of ultrasonic energy is able to hear the audio signal while others outside the beam are unable to hear the signal or may hear it at a low level. The audible frequencies associated with the audio signal are created by interactions between different frequencies carried in the ultrasonic beam and air molecules which respond non-linearly to the ultrasonic frequencies. 1The product names used are for identification purposes only. All trademarks and registered trademarks are the property of their respective owners.
A related system is described in Austin Lowrey III, Apparatus and method of broadcasting audible sound using ultrasonic sound as a carrier, U.S. Pat. No. 6,052,336. Another system with similar goals is described in Wayne B Brunkan, Hearing system, U.S. Pat. No. 4,877,027.
Networks allowing the transmission of data are well known. Networks that are associated with mobile devices are well known, and examples are abundant. For example, a cellular telephone system is a network that allows mobile users to transmit and receive data, including, for example, digitized voice transmissions, text messages and other data. Other forms of wireless networking allow processor based devices of various type to intercommunicate with each other and with other networks, including for one example a wireless network that complies with the 802.11 family of standards. See for example, ISO/IEC 8802-11:1999(E) ANSI/IEEE Std 802.11. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, 1 edition, 1999.
Some mobile device networks are persistent, that is, a node stays in a network as long as it is in the vicinity of a network access point and is operating; others may be spontaneous and short lived. For one instance a device may form a spontaneous, temporary network with another device when two devices are proximal and then disconnect when either device moves away, only to form another spontaneous network.
Locating devices are also well known. A common example of a locating device is a GPS receiver; because of the common knowledge of GPS receivers, this type of locating device is not further described here, except to note that GPS receivers work better outdoors, in general, than indoors.
Other forms of locating devices that work indoors or within a bounded area are also well known. Several classes of locating devices based on a radio source at the device or a radio-responsive circuit at the device are known. For one example, a cellular phone may be locatable based on the signal emitted by the cellular phone and its reception by locators. A wireless device such an 802.11 class transceiver on a wireless network may be similarly located. Even an un-powered device that has a Radio-Frequency Identification (RFID) circuit as a component may be locatable by other devices able to activate and read a signal from the activated RFID circuit.